I'd say of all the things Anker its really hard right now to get to 1 product but I'd score them:
Best Audio: Soundbuds Slim , followed by the Life
Best battery: Powercore 10000, followed by the Powercore+ Mini
Best charger: close one but probably the Powerport5 USB-C followed by the Powerport4.
Not sure I'd be able to get to just 1 thing but it would be a toss between the Slim and the 10000 basically if either got lost/destroyed I'd buy another right away, just way too good and useful to have them constantly. Being able to never to hold a phone to your head and so be hands-free and never have a flat anything despite the worst possible day, is just liberating.